Safety Relays - Where and How They Work
Safety Relays are devices that implement safety functions. In the event of a hazard, a safety relay will work to reduce to risk to an acceptable level. When an error occurs, the safety relay will initiate a safe and reliable response. Each safety relay monitors a specific function. By connecting them to other safety relays, one can achieve total monitoring of a machine or plant. Safety relays are a simple and efficient way to meet existing safety standards, resulting in safe operation for your personnel and equipment as well as a long service life. Risk reduction should be a priority for any business, to both protect its employees and reduce the possibility of costly accidents or equipment replacement. Generally, if a risk is able to be reduced, then it should be.

Some functions of safety relays include:
  • Stopping a movement in a controlled and safe manner.
  • Monitoring the position of movable guards.
  • Interrupting a closing movement during access.
  • Emergency off/stop.


Operating a Safety Relay
Safety relays are simple to operate and have a clear structure. Because of this, their use does not require any specific training measures. Generally, all that is needed to successfully operate a safety relay is some general electrical knowledge and some awareness of the standards required in your particular situation. The use of safety relays has become widespread due to their compact design, high reliability, and most importantly; the fact that they meet all of the required standards. They have become an integral component of any new plant or machine where safety functions are necessary. Today, safety relays are available for practically every requirement imaginable. A phoenix contact safety relay wiring diagram
Safety Relays in the Field
Safety Relays are commonly used in control devices, such as:
  • Light Curtains: Light Curtains act as a sort of tripwire and are used to protect personnel in the vicinity of moving machinery with the potential to cause harm. When any of the infrared beams generated by the device are broken, a stop signal is sent to the relevant equipment. Light curtains will typically be connected to a safety relay, which will then handle the actual process of removing the motive power from the hazard. Some safety relays may also be equipped with a muting functionality, which enables the temporary disabling of the safety function. For example, when used with light curtains, muting can allow objects to pass through the curtains without tripping the safety relay.
  • Safety Mats: Pressure-sensitive safety relays can be used in conjunction with safety mats to ensure the safety of personnel, and further supplement other safety devices. For example, one may setup a set of light curtains to allow objects to pass through it while the safety mat is activated, allowing access to load or unload a machine. Safety mats are also usable as an independent safety measure. Just like light curtains, they can be configured to initiate a stop command when activated.
  • Three-position Devices: Safety devices such as a three-position device can be essential when troubleshooting an application, and there is a variety of devices in this category. Three-position devices often feature a pressure-sensitive joystick that is held in a particular position to operate, and when the user lets go of the joystick, it will return to the default stop position.
  • Two-hand Control Devices: A two-hand control device is essential for operations that require a high degree of safety consideration. Such devices are crucial when you want to prevent the operator from being able to reach into the hazardous area. When the device is out of reach from the operator controls, a one-handed control device can suffice instead.
  • Magnetic Switches: A magnetic switch is useful in applications where it is crucial for a door or hatch to be closed or for two objects to intersect or be aligned with each other. When contact between the two sensors is lost, an emergency stop signal can be sent to the appropriate relay to safely stop the machine from operating. Magnetic switches are very compact which allows for easy positioning or hiding when used in gates or switches. Because no mechanical contact is needed for operation, a magnetic switch will often tout a long operational lifetime. Water, dirt, and dust do not affect magnetic switches, allowing for their use in a variety of environments and conditions.
  • Emergency Stop Buttons: Emergency Stop buttons (also known as E-stop) is used to stop a machine when it is breaking down if when someone is in danger. All E-stop buttons should be red with a yellow housing. Some emergency stop buttons will also feature an emergency grab wire, allowing interaction with the stop interface even when at a distance from the button itself. The grab wire should also be red for easy identification.
  • Non-contact Safety Sensors: Similar to a magnetic switch, a non-contact safety sensor is ideal to use when it is crucial for segments to be aligned but when they do not have to be in direct contact, unlike with a magnetic switch. Some of these sensors will also allow for multiple sensors to be used in conjunction, allowing for a more precise configuration when necessary.
  • Interlock Safety Switches: An interlock safety switch is used to detect when components are locked together, and can also be used to hold them in place until certain parameters are met, such as completion of an operation. This can be achieved in several different ways, such as a spring lock or locking itself when a specified position occurs.
Pilz Safety Relays
Jokab Safety Relays
Pilz Contact Expansion Safety Relay
Safety Relay Product Overview Video